- Boost-users - lists.boost.org

[units] unit conversion on construction in relation to argument passing
by alfC 25 Mar '11

25 Mar '11

Hi, Boost.Units offers automatic conversion (if conversion factor is defined) on construction of variables: quantity<cgs::lengh> A = 4.*cgs::centimeter; quantity<si::length> a(A); nice! But for some reason I believe this would work for argument functions double f(quantity<si::length> v){ return 1.;} ... quantity<cgs::lengh> A = 4.*cgs::centimeter f(A); // doesn't work! not matching function why is this? isn't the argument of the call a sort of construction argument for the function argument, or is more like a plain assignment. Is there a way to force the automatic conversion of the function call. Or I am forced to use this other long call? f(quantity<si::length>(A)); Thanks Alfredo Full code: #include<boost/units/systems/si.hpp> #include<boost/units/systems/cgs.hpp> double f(quantity<si::length> v){ return 1.; } int main(){ quantity<cgs::length> A(4.*cgs::centimeter); f(A); //not matching function return 0; }

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Assertion `!pthread_mutex_destroy(&m)' failed.
by Panagiotis Foteinos 25 Mar '11

25 Mar '11

Hello users. I am new to boost:threads, so my apologies in advance. I am getting an assertion failure right before main() exits. Specifically, I get the following error: "*/usr/include/boost/thread/pthread/mutex.hpp:45: boost::mutex::~mutex(): Assertion `!pthread_mutex_destroy(&m)' failed.*" Below is the code snippet: *********************************************************************************************************************************** class Test { private: boost::mutex mtx; public: int counter; Test() { counter = 10; } void DoWork() { for(unsigned int i = 0; i < 1000000; i++) { mtx.try_lock(); counter++; mtx.unlock(); } } }; int main() { unsigned int N = 7; boost::thread* test_threads = new thread_type[N]; for(unsigned int i = 0; i < N; i++) { test_threads[i] = thread_type(boost::lambda::bind<void>(&Test::insert, &object)); } for(unsigned int i = 0; i < N; i++) { test_threads[i].join(); } return 1; } *********************************************************************************************************************************** Can somebody shed some light? Main() exits normally, if I replace mtx.try_lock() with mtx.lock(). Why this behavior? Best Regards, Panagiotis Foteinos

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Fw: Boost.thread - infinite thread and expired thread object
by Emil Kaffeshop 25 Mar '11

25 Mar '11

--- On Fri, 3/25/11, Emil Kaffeshop <emildg(a)yahoo.com> wrote: > From: Emil Kaffeshop <emildg(a)yahoo.com> > Subject: Boost.thread - infinite thread and expired thread object > To: boost-users(a)lists.boost.org > Date: Friday, March 25, 2011, 7:16 PM > Hello all, > > I am new to the group and boost. > > I have a question. > > void f (void) > { > while (1) > { > //do thread job > } > } > > void start_thread () > { > boost::thread t(f); > } > > void main (void) > { > start_thread (); > pthread_exit (NULL); > } > > What are consequence for the thread "f" from disappearing > of thread object? > Does thread specific data available? > Does boost::this_thread functions available? > So is there something which f needs from "t" object? > > Thank you in advance! > > Best Regards > > > >

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Connecting Windows Messages/Events with Boost callbacks
by asif saeed 25 Mar '11

25 Mar '11

Hi, I recall sometime back someone posted this question on this list and the response/answer was very good. Could someone please provide link to that earlier post? Or, alternatively, could you please post the solution again? Best regards / Asif

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Re: [Boost-users] Collecting boost multi-index meta data
by Joaquin M Lopez Munoz 25 Mar '11

25 Mar '11

Gokulakannan Somasundaram <gokul007 <at> gmail.com> writes: > > > Hi, > Say i have a boost::tuple / MPL Sequence, on which i have > created a multi-index. Is it possible for me collect all the > attribute numbers on which i have declared the > IndexSpecifierList( the one passed as template parameter to > boost::multi_index::indexed_by ) ? Hi Gokul, I'm not sure I undersand your question. Have you taken a look at the index_type_list nested type? http://www.boost.org/libs/multi_index/doc/reference/multi_index_container.h… types >From this MPL sequence you can easily extract the list of key extractor types used for defining the multi_index_container, which hopefully is close to what you're after. Don't hesitate to elaborate a little more on your question and I'll see whether I can be more helpful. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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Math/Statistical Distributions
by Andrej van der Zee 25 Mar '11

25 Mar '11

Hi, Statistics have been a while ago... I was reading the documentation, at least part of it, of the Boost library Math/Statistical Distributions. But I think I need a bit of help... I have many values Yi that are closely distributed around a mean value Y-mean. The collection of Yi is obtained by an algorithm that sometimes produces trash values that need to be discarded. Such false values are typically not "close" to the Y-mean. I was hoping somebody could tell what distribution I should use and how I should use this. If I recall correctly from my school-days, I need the Normal (Gaussian) Distribution. What would be the algorithm to find those trash values? Thank you, Andrej

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Serialization: multiple definition of 'boost::archive::detail::init_guid...
by Marco Piacentini 25 Mar '11

25 Mar '11

Hi guys...I've found on google some people with the same problem, but all of them have a partial solution... In practice this error happens where I include a .h file which contain the directive #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> and the macro BOOST_CLASS_EXPORT() in more than one .cpp file... I have the necessity to serialize/deserialize in more than one .cpp file and at these points I have to include the .h which contains the polymorphic struct that I have to serialize/deserialize. So the partial solution proposed from others to put all the the include in a single file, is not praticable for me.. Do you know another solution?thank you very much... Bye..

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Boost Threads are not parallel
by Panagiotis Foteinos 25 Mar '11

25 Mar '11

Hello users. I observed the boost threads behave strangely, depending on the way I call the function to be executed in parallel. In the following example (example #1), the threads launched are executed in parallel: **************************************************************************************** 1) class Test { int insert(){}; } object; boost::thread* threads = new boost::thread[N]; for(unsigned int i = 0; i < N; i++) { threads[i] = boost::thread(&Test::insert, &object); } **************************************************************************************** However, in the following example (example #2), the threads are executed sequentially. Only the line in the for-loop body differs from example#1. **************************************************************************************** 2) class Test { int insert(){}; } object; boost::thread* threads = new boost::thread[N]; int ret; for(unsigned int i = 0; i < N; i++) { threads[i] = boost::thread(boost::lambda::var(ret) = object.insert()); } **************************************************************************************** Can anybody explain why the threads in example#2 are executed sequentially (i.e., one at a time)? Best Regards, Panagiotis Foteinos

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io_service::stop() call safe from within post()ed functor?
by Dom Driver 25 Mar '11

25 Mar '11

Hi guys, Picture a server class with the following methods (pseudocode): void Server::Work() { // Start the Async receive. mSocket.async_receive_from( *blah* ) ); // Start the Async IO service. mASIOService.run(); } void Server::Start() { // Launch a new thread to do the work. mThread = boost::thread( boost::bind( &Server::Work, this ) ); } void Server::Stop() { // Post the stop request to the io_service. mASIOService.post( boost::bind( &Server::DoStop, this ) ); // Join the comms thread. mThread.join(); } void Server::DoStop() { // Actually stop the io_service. mASIOService.stop(); } Assuming handling of packets is all correctly implemented, is it safe for the user to simply call the Stop() object method to stop the server? Basically, can a function that's been post()ed to an io_service call io_service.stop() for that io_service? TIA, Dom

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[iostreams] Can I apply different char_type on a chain of filters?
by 甜瓜 25 Mar '11

25 Mar '11

Hi, all, I usually want to read a file, and group the bytes into some object (eg: struct MyData) for further use. boost::iostreams provides the filtering_stream, but it seems all filters along the chain MUST have the same char_type. Is there a way that transform a byte stream into MyData stream? eg: ifstream file("d.gz", ios_base::in | ios_base::binary); filtering_streambuf<input> in; in.push(MyDataExtractor()); in.push(gzip_decompressor()); in.push(file); class MyDataExtractor { public: typedef MyData char_type; struct category ...; template<typename Source> std::streamsize read(Source& src, char_type* s, std::streamsize n) {...} }; Thank you in advance! -- melon

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